Nitriles such as acrylonitrile and methacrylonitrile have long been industrially produced as important intermediates for the preparation of synthetic fibers, synthetic resins, synthetic rubbers and the like. A major use of acrylonitrile is in the form of fibers. Acrylonitrile-butadiene-styrene terpolymers (ABS) are important thermoplastic structural plastics. Nitrile-type rubbers, first commercialized as the German Buna-N type in 1930, are copolymers of acrylonitrile and a diene, usually butadiene.
The currently practiced commercial processes for the production of nitriles, such as acrylonitrile and methacrylonitrile, subject an alkene, i.e., propylene or isobutene, to reaction in a gas phase with ammonia and oxygen in the presence of a catalyst at a high temperature. Generally, the catalyst formulations employed are proprietary to the catalyst supplier, but the technology is well established. Furthermore, it is known to include additional starting materials, including additional reactants, such as molecular oxygen and/or steam, gas, and inert materials, such as nitrogen and carbon dioxide, along with the hydrocarbon starting material.
In view of the relative abundance of lower alkanes relative to corresponding alkenes, resulting in price differences particularly between propane and propylene or between isobutane and isobutene, attention has been drawn to developing improved catalysts for producing nitriles from these, less expensive, lower alkanes. Propane or isobutane is used as starting material in an ammoxidation reaction with ammonia and oxygen in a gas phase in the presence of a catalyst.
Catalysts containing molybdenum, vanadium, antimony and niobium which have been shown to be effective for conversion of propane to acrylonitrile and isobutane to methacrylonitrile (via an ammoxidation reaction) and methods of preparation of said catalysts are described in numerous publications, patents and patent applications. See, for example, U.S. Pat. No. 5,750,760 to Ushikubo et al., U.S. Pat. No. 6,036,880 to Komada et al., U.S. Pat. No. 6,143,916 to Hinago et al., and U.S. Pat. No. 6,514,902 to Inoue et al.
Oxide catalysts containing molybdenum, tellurium, vanadium, and niobium and methods of preparation of said catalysts are described in U.S. Pat. No. 5,049,692, U.S. Pat. No. 5,231,214, U.S. Pat. No. 5,281,745, U.S. Pat. No. 5,380,933, and U.S. Pat. No. 5,422,328. Further, oxide catalysts containing molybdenum, vanadium, niobium, and antimony are described, for example, U.S. Pat. No. 4,760,159, U.S. Pat. No. 4,797,381, and U.S. Pat. No. 7,087,551.
The methods of preparation of said catalysts can generally be divided in two categories, namely, hydrothermal and non-hydrothermal. In the so-called hydrothermal route generally an aqueous mixture of ingredients is treated at an elevated temperature (e.g., 150-250° C.) and elevated pressure (e.g., 200-300 psig) to presumably form mixed oxide catalytic phases. In the non-hydrothermal route generally an aqueous mixture of ingredients is treated at a temperature generally less than 100° C. at ambient pressure followed by drying to prepare a catalyst precursor. The catalyst precursor is heat treated or calcined to form the catalytic phases. For example, U.S. Pat. No. 5,750,760, U.S. Pat. No. 6,514,902, U.S. Pat. No. 6,610,629, U.S. Pat. No. 7,087,551, U.S. Pat. No. 7,109,144, US and EP 1,632,287, EP 1,806,178, and WO 2007/119376 disclose methods of non-hydrothermal preparation of catalyst compositions comprising molybdenum, vanadium, antimony, and niobium as component metals. U.S. Pat. No. 5,750,760 discloses a method of preparing an aqueous solution of a precursor to an oxide catalyst of the empirical formula MoaVbSbcXxOn (wherein X is at least one element selected from the group consisting of Nb, Ta, W, Ti, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, B, In, Ce, an alkali metal and an alkaline earth metal) as (1) a method of adding and mixing a compound containing Mo and a compound containing an element represented by X to an aqueous solution containing V component and Sb component to obtain an aqueous solution, or (2) a method of adding and mixing a compound containing V and a compound containing an element represented by X to an aqueous solution containing a Mo component and a Sb component to obtain an aqueous solution. U.S. Pat. No. 6,514,902 discloses a process of making an oxide catalyst comprising a compound oxide containing Mo, V, and Sb as essential component elements which process comprises subjecting a solution or slurry, in water and/or alcohol, of a raw material mixture comprising a Mo compound, a V compound, and an Sb compound as essential raw materials to a specific oxidation treatment using an oxidizing gas and/or an oxidizing liquid before subjecting the solution or slurry to drying and subsequent calcination. Catalysts made by the methods described above do not provide adequate selectivity and yield required for a commercial application.
It is an object of the invention to provide catalysts for the selective oxidation and ammoxidation of alkanes and methods to make said catalysts.